1. Field of the Invention
The present invention relates to a control member for threading tube lifters in crocket galloon looms, of the type comprising an electromagnet which is fixed with respect to a thread guide rail and associated with at least a lifter oscillatably engaged in relation to said thread guide rail, said electromagnet being energizable to bring the lifter from a disengagement condition in which the latter keeps a fixed positioning with respect to the thread guide rail, to an engagement condition in which it can be engaged by actuator means giving it an oscillating motion in synchronism with the oscillating motions performed by the thread guide rail.
The present control member particularly lends itself to be used on crocket galloon looms provided with a jacquard device, but it can also be applied to needle looms to make ribbons as welll as to traditional and dobby looms.
2. Prior Art
It is known that in crocket galloon looms provided with a jacquard device each weft yarn is engaged through a threading tube oscillatably supported by a thread guide rail which in turn is oscillatably movable in synchronism with the needle movements. Each threading tube can be selectively operated, upon command of the jacquard device, so that it performs suitable oscillations with respect to the thread guide rail causing the respective weft yarn to be selectively engaged or not by one or more needles during each working cycle.
By selectively operating the threading tubes during each working cycle, the jacquard device is capable of controlling the positioning of the single weft yarns so as to produce very elaborate figured fabrics.
Operation of the threading tubes is carried out through control lifters connected thereto by means of cables guided along respective sheaths. Lifters are individually operable upon command of selector means being part of the jacquard device.
In modern technical solutions lifters are connected to the thread guide rail along which they are distributed in an upright position, each of them being located over the respective threading tube. Also associated with the thread guide rail is actuator means provided with an oscillatory motion in a vertical direction, which motion is added to the oscillations performed by the thread guide rail.
Associated with each filter is an electromagnet which, upon command of an electronic control unit suitably programmed, is capable, if necessary, of positioning the lifter so that it may be engaged by the actuator means and involved in the oscillatory motion thereof in order to operate the respective threading tube.
Generally when the corresponding magnet is deenergized, the lifter is disposed in a disengagement condition and it is only subjected, together with the respective threading tube, to the horizontal and vertical oscillations of the thread guide rail as it is not engaged by the actuator means. When the electromagnet is energized, the lifter is slightly shifted with respect to the previously taken position and is disposed in an engagement condition. Under this situation the lifter can be engaged by the actuator means in the region of an end projection thereof, so that it can be vertically translated against the action of a return spring and can cause an oscillation of the respective threading tube with respect to the thread guide rail during each working cycle that it performs in this condition.
Presently each lifter is guided during the vertical translations it receives from the actuator means, by one or more guide elements which are fixed with respect to the thread guide rail. The displacements of the lifter from a disengagement condition to an engagement condition usually take place as a result of the elastic deformation of the lifter itself under the effect of the magnetic field created by the energized electromagnet. When the electromagnet energization ceases the lifter, due to its elastic return, is automatically arranged in its disengagement condition.
However the above described solutions are not reliable in the long run as regards the correct operation of the lifter.
This is partly due the fact that when the lifter is in its engagement condition it is elastically deformed and exerts a stress on the corresponding guide element. Under this situation the guide element can be rapidly worn due to the slidings of the lifter as a result of its vertical oscillations.
Reliability in operation is also impaired by the fact that lifters must be operated using very small electromagnets in order to achieve a reduced bulkiness. When after a prolonged use of the knitting machine dust and other impurities have laid down on the electromagnets, the magnetic field they produce may become too weak and therefore unable to bring about the elastic deformation of the corresponding lifters.